1. Technical Field
This invention relates to the field of percutaneous access to the vascular system. More specifically, this invention relates to an apparatus and system for percutaneous access to a vessel of a patient when initial entry is made with a small gauge needle.
2. Background Information
Many medical procedures require the percutaneous placement of an interventional medical device, such as a catheter, into an artery or vein. Among others, such interventional devices may be used in connection with blood pressure monitoring, blood sampling, and the administration of drugs and fluids to a patient.
Typically, such devices are introduced using the well-known Seldinger technique. The Seldinger technique for percutaneous entry into the vascular system has been in widespread use in diagnostic and interventional medicine for many years. In the Seldinger technique, the physician makes an oblique entry into the artery or vein with a beveled needle. A wire guide is introduced into the proximal end of the needle, and passes through the length of the needle into the artery or vein. The needle is thereafter withdrawn, leaving the wire guide in place. The catheter or other interventional device is then passed over the wire guide, through the puncture, and into the artery or vein at the needle puncture site. Once the catheter is in place, the wire guide may be withdrawn.
One of the disadvantages of this procedure is that the initial needle stick must normally be made with a needle that is large enough to accept the wire guide through its central bore. Conventional wire guides are often comprised of a tightly wound helical stainless steel wire coil. In order to have sufficient rigidity to properly support and lead many standard catheters and other interventional devices, such wire guides are typically constructed to have an outer diameter in the range of about 0.035 to 0.038 inch (0.89 to 0.97 mm). A wire guide having this diameter will pass through an 18 gauge thinwall needle. An 18 gauge needle typically has a 0.050 inch (1.27 mm) outer diameter and a 0.042 inch (1.07 mm) inner diameter (I.D.).
The 18 gauge needle is the most commonly used needle for initial vascular access, and has become the standard needle for use with the Seldinger technique for percutaneous catheterization. However, the outer diameter of an 18 gauge needle is just large enough to damage tissue or cause excessive bleeding if it does not enter the vessel correctly, or if it inadvertently penetrates some other organ. As a result, it is desirable to utilize a smaller gauge needle to effect the initial entry. Smaller needles such as 21 gauge thin wall down to 24 gauge thin wall are considered small enough so as not to cause damage to tissue or organs, or cause excessive bleeding if inserted off target. A 21 gauge thin wall needle typically has a 0.032 inch (0.81 mm) outer diameter (O.D.) and a 0.022 inch (0.55 mm) inner diameter (I.D.). A 24 gauge thin wall needle typically has a 0.022 inch (0.55 mm) O.D., and a 0.014 inch (0.35 mm) I.D.
In addition to their smaller diameters, smaller gauge needles typically have a correspondingly shorter bevel at the needle tip compared to the lengthier bevel tip of an 18 gauge needle. It is much easier to get a short bevel into the lumen of a small vessel than the longer bevel of the type found in an 18 gauge needle. However, the respective bores of smaller needles, such as 21 to 24 gauge needles, are not large enough to pass a standard 0.035 inch or 0.038 inch (0.89 mm or 0.97 mm) diameter wire guide therethrough. Generally a wire guide of 0.018 inch, or smaller, is required to pass through the bore of such small diameter needles. However, as stated, many diagnostic and interventional devices require at least a 0.035 inch (0.89 mm), and more preferably a 0.038 inch (0.97 mm), diameter wire for optimal introduction and manipulation through the vasculature.
U.S. Pat. No. 4,650,472, assigned to the assignee herein, discloses a catheterization apparatus which allows a smaller gauge needle, such as a 22 gauge needle, to be used for the initial puncture through the skin of the patient in place of the conventional 18 gauge needle. A 22 gauge needle typically has a 0.028 inch (0.71 mm) O.D. and a 0.019 inch (0.48 mm) I.D. This patent is incorporated by reference herein. A 0.018 inch (0.46 mm) outer diameter wire guide is inserted through the bore of the 22 gauge needle. In the apparatus described in the patent, a removable inner sleeve is provided over the wire guide but inside the outer sleeve portion of the apparatus. This removable inner sleeve has a tapered tip which extends through the distal opening of the outer sleeve, and provides a smooth diametrical transition between the large distal opening of the outer sleeve and the 0.018 inch wire guide. The inner sleeve is generally about 0.038 inch (0.97 mm) O.D., and the outer sleeve is tapered to fit over the inner sleeve. The outer sleeve and the inner sleeve are inserted into the blood vessel in tandem. The smooth diametrical transition of the leading end of this tandem minimizes the trauma that may otherwise be caused by the insertion of the large diameter outer sleeve over the small diameter wire guide. Once the outer sleeve is properly positioned within the blood vessel, the inner sleeve and the smaller wire guide can be withdrawn, leaving the outer sleeve in place. If desired, a larger (0.035 to 0.038 inch) (0.89 to 0.97 mm) wire guide can then be introduced through the outer sleeve and into the vessel. The outer sleeve can thereafter be removed from the patient, leaving the larger wire guide in the vessel ready to accept a catheter or other interventional device, as in the standard Seldinger technique. An example of such an introducer system is the MICROPUNCTURE® introducer set, available from Cook Incorporated, of Bloomington, Ind.
The apparatus disclosed in the '472 patent has been successfully used to percutaneously insert a catheter into a blood vessel using a wire guide and an introducer needle which are much smaller in diameter than the distal opening of the catheter. This ensures good flow characteristics for the catheter and a minimum of tissue trauma to the patient. It also allows for the introduction of larger diagnostic and interventional devices than would otherwise be possible when an initial entry is made with a small diameter needle.
In some cases when a catheter is to be inserted using a small gauge needle, such as a needle of the type described in the '472 patent, it is necessary to make the puncture through tough, fibrous tissue. Examples of such tissue are scar tissue, muscle tissue and the like. In such cases it is sometimes desired to further enhance the rigidity or column strength of the disclosed two-part dilator system, so that the apparatus can be more easily pushed through the puncture site and the vessel wall, and yet still be flexible enough so that additional trauma is not caused to the vessel wall when the device enters the vessel. In order to enhance the rigidity of the dilator system, it is known to position a stiffening cannula, such as a thin stainless hypodermic needle cannula, within the lumen of the inner sleeve of the apparatus of the '472 patent. The stiffening cannula generally extends from the proximal end of the apparatus and ends just short of the distal tip taper of the inner sleeve. Since the tip taper of the inner sleeve is not reinforced by the stiffening cannula, it thereby retains its flexibility. The stiffening cannula provides extra stiffness to the main body of the apparatus without adding significant bulk, complexity or additional parts. An example of such an introducer system is the MICROPUNCTURE® PUSH-PLUS™ introducer set, available from Cook Incorporated, of Bloomington, Ind.
The use of a stiffening cannula has worked fairly well when needles on the larger end of this system, such as 21 gauge needles, are utilized. However, as the systems get smaller (e.g., 22, 23 and 24 gauge needles), the stiffening cannula may protrude through the tapered distal end of the inner sleeve when the inner sleeve is pushed through the tough, fibrous tissue. As a result, the stiffening cannula may directly access the vessel and tissue. In this event, considerable trauma can be caused to the vessel wall and tissue due to the lack of flexibility of the hard, stiffening cannula. This can also even be a problem with some larger non-stiffened systems when they encounter scar tissue or calcifications during introduction.
There exists a need for a percutaneous insertion apparatus for an interventional device that can utilize small needles on the order of 22, 23 or 24 gauge, or smaller, for the initial insertion through the skin of the patient, and wherein the components of the system have sufficient stiffness to allow the insertion apparatus to be pushed through tough, fibrous tissue without directly exposing the tissue to trauma resulting from the use of stiff components.